Venus is the Earth-that-could-have-been and the Earth-that-still-might-be. Our so called sister planet orbits second from the Sun. Cloudy, hot, and unhospitable to life as we know it, Venus demonstrates as well as Mars why comparative planetary science can greatly improve understanding of our own planet.
The greenhouse effect on Venus results in a poorly understood phenomena called zonal super-rotation. Hurricane winds across the cloud tops help the atmosphere to rotate much faster than the planet itself, but these winds give way to barely a breeze at the surface. The atmosphere is primarily carbon dioxide with some nitrogen. Thick sulfur dioxide clouds and other particulates conspire to hide the surface. The USSR visited the surface of Venus with several landers, some that included cameras, while orbiters with radar equipment accomplished global surface mapping last decade by orbiters. Mountains, volcanoes, pancake domes, plains, channels, and a impact craters have been discovered on the surface. The surface appears to be geologically young, despite little evidence for plate tectonics, the process on the Earth that recycles old crust and exudes new crust. The youthfulness of the Venusian surface may be due to catastrophic upheavals that periodically see the crust overturned (this might have last occurred from 300 to 500 million years ago).
Credit: JPL/NASA – “Volcano Sapas Mons“
The European Space Agency’s Venus Express is the latest mission to Venus and still ongoing. The orbiter has been tasked with several years of cloud and atmospheric studies and has already discovered a level of complexity in the clouds that had not been previously seen. “Boiling” clouds at low latitudes become streaky clouds at mid latitudes. At the poles thick and uniform clouds are interrupted rarely by darker streaks. At both poles there are huge vortexes in the cloud decks with mysterious features that resemble the eye of a hurricane that constantly changes shape.
Credit: ESA/MPS/DLR/IDA – “False-colour ultraviolet image of the Southern hemisphere of Venus“
Now in an extended mission, Venus Express in July 2008 began a series of maneuvers to bring it closer to Venus.
The history of Venus remains a mystery. Was it ever more like Earth, and if so, what happened? Why does the surface appear to be geologically young, and what is creating the sulfuric acid and other particulates in the atmosphere? Could life exist in more temperate zones in the clouds?
Answering these questions will in turn tell us more about the Earth. Venus, perhaps, provides a snapshot of our own future, if our greenhouse effect were to speed away out of our control. Knowing more about the end result could help us avoid the same fate.